Polyolefin pipe

ABSTRACT

This invention relates to a polymeric pipe, and more particularly a polymeric pipe where the pipe comprises a crosslinked polyolefin formed from extruded polyolefin comprising a photoinitiator and a reactive extrusion species. More particularly, this invention relates to the manufacturing of plastic pipes and tubing by utilizing co-rotating twin screw extrusion combined with photo-induced crosslinking, of thermoplastic polymers such as polyethylene, to produce PEX pipes and tubing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase application under 35 U.S.C. 371 ofInternational Application No. PCT/EP2014/058218, filed Apr. 23, 2014,which claims priority to and the benefit of U.S. Provisional ApplicationNo. 61/819,038, filed May 3, 2013, the disclosures of each of which areincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to a polymeric pipe, and more particularly apolymeric pipe where the pipe comprises a crosslinked polyolefin formedfrom extruded polyolefin comprising photoinitiator. The invention alsorelates to a polymeric pipe where the pipe also comprises a scavenger;and/or co-agent and a stabilizer; this is sometimes referred to as aco-agent and/or stabilizer package. More particularly, this inventionrelates to the manufacturing of plastic pipes and tubing by utilizingco-rotating twin screw extrusion combined with photo-inducedcrosslinking, of polyolefinic polymers such as polyethylene, to producecrosslinked polyethylene (PEX) pipes and tubing. The pipes are intendedto be used in cold (e.g. potable) or hot water applications. They areparticularly suitable for cold water application since they may exceedall current standards for drinking water transmission.

BACKGROUND

Extruded pipes made from polyolefin polymers are well known for avariety of industrial applications. Typically they are used in thebuilding industry for domestic (e.g. potable) water pipes, radiatorpipes, floor-heating pipes and for similar applications in ship buildingetc. Such pipes can also be used as district heating pipes and asprocess pipes in the food industry etc. Other applications include theconveyance of gaseous fluids and slurries.

The polyolefin used in extruded pipes is often crosslinked, as thisprovides a number of advantages. Such advantages include, but are notlimited to, long term stability including oxidation resistance, whichassists in meeting current codes and standards for potable waterapplications, flexibility in installation including a “memory effect”,etc. Crosslinked polyethylene (PEX) is commonly used for plastic pipes.There are several varieties of PEX that utilize a number of differentcrosslinking chemistries and processing technologies. Various PEX gradesfurther contain other additives such as antioxidants and/or stabilizerpackages in different concentrations and combinations. Three knownvarieties of PEX for pipe applications are PEX-a, PEX-b, and PEX-c.

In the PEX-a process (“Engel Method”), the cross-linking is induced byperoxide under the influence of heat and high pressure. The resultantPEX-a composition is crosslinked through carbon-carbon bonds to form thecross-linked polymer network. The PEX-a crosslinking process occurs inthe melted stage, as opposed to the primary crosslinking processes forPEX-b and PEX-c. The primary reaction is the formation of free radicalsupon decomposition of the peroxide, which has to be present bydefinition for PEX-a, and subsequently, the free radical abstractshydrogens from the PE polymer chains. The latter gives new carbonradicals, which next combines with neighboring PE chains to form stablecarbon-carbon bonds, i.e., crosslinks. The crosslinking, which isconsidered to be homogeneous and uniform for PEX-a, gives degrees ofcrosslinking (typically referred to as CCL) in the range of 70-90% forpractical applications. Requirement for CCL is to be above 70% for PEX-aas defined in ASTM International Standard for Crosslinked Polyethylene(PEX) Tubing, F 876-10 (approved Feb. 1, 2010). The PEX-a process maytherefore be used to produce good quality pipes.

In the PEX-b process, the crosslinking is induced by moisture and heatover extended pre-determined times typically conducted in a “Saunaatmosphere”. The most commonly used methods are referred to as theSioplas (two-steps), and the Monosil (one step) methods, respectively.In the Sioplas method, a silane, such as for example a vinylsilane isgrafted to a HDPE resin prior to pipe extrusion. In the Monosil method,a silane is blended with the HDPE resin during pipe extrusion. In bothmethods, which are chemically different in the pre-crosslinking steps,the fundamental principle for the actual crosslinking are practicallyidentical, i.e., the crosslinking occurs in a secondary post-extrusionprocess that is accelerated by a combination of heat and moisture. Thelatter combination is the active “reagent”, which is involved in theprimary hydrolysis and condensation reaction. In principle, the extrudedpipe is exposed to hot water and a steam bath. A fundamental differenceto PEX-a, is that for PEX-b, the resultant crosslinks are not betweencarbon-carbon bonds, but instead, oxygen-silicon covalent bonds(siloxane “bridges”) are formed. In comparison with PEX-a, the crosslinkdensity (CCL) are somewhat lower for PEX-b (65-70%), and thecrosslinking is also less uniform.

In the PEX-c process, the crosslinking is commonly referred to as a“cold” method. In the PEX-c process, no chemicals are needed in order tofacilitate the crosslinking process, but instead high energy electronbeam (EB) irradiation is utilized to create the free radicals necessaryfor the hydrogen abstraction and subsequent crosslinking to take place.The high energy electron beams are non-selective, i.e., chemical bondsare cleaved in an un-controlled fashion. The latter has the consequenceof creating side reactions, together with the reaction aimed for, i.e.,the crosslinking of HDPE. The crosslinking density for PEX-c istypically in the 70-75% range, and caution has to be taken withirradiation time since a too long exposure may give discolored productsand/or brittleness. PEX-c has been successfully used for many yearsdespite the somewhat challenging production conditions.

Another possible crosslinking process is ultra violet (UV) curing, i.e.,photoinduced crosslinking, where a pipe formulation comprising acombination of a polyolefinic polymer such for example polyethylene, aphotoinitiator, a co-agent, and a stabilizer package, is exposed to UVradiation to form a crosslinked polymer. In the case where polyethyleneis utilized, the final product is a PEX pipe. UV curing is generallyconsidered to be a “green” and environmentally friendly technology,since no solvents are used in the process and no emission of volatilechemicals takes place.

One major challenge that occurs with all extruded pipes used fordrinking water applications is the potential issue with leaching of thevarious additives from the polymer pipe matrix. The various additiveswhich include initiators, stabilisers, co-agents, processing aids,antioxidants, etc. may leach from the polymer matrix over time and canbecome available to contaminate the fluid contents flowing within thepipe. This problem is a particular issue in cases such as drinking waterapplications and industry standards exist which quantify the allowablesafe levels of leaching of materials from the pipe over a period of timefor such applications. The various additives are required to be presentin the pipe when manufacturing it in order to facilitate processing ofthe pipe when extruding the raw material polymer and also to ensurestructural integrity and resistance to ageing etc. of the finished pipe.At the same time, the very presence of these materials presents achallenge since these materials may leach from the polymer matrix over aperiod of time.

The use of plastics pipes in drinking water applications is a challengeas described above. One difficulty is the requirement to find the rightstabiliser or combination of stabilizers that gives sufficient long-termstability. One measure of this stability is chlorine resistanceaccording to the standard ASTM F2023. At the same time, the stabilizers,anti-oxidants, photoinitiators, co-agents, and other additives, shouldnot generate too high levels of remaining residuals in the final pipeproducts, which would make it impossible to meet the standards requiredfor drinking water pipes (in North America this is the NSF 61 standard).However, we have found a novel combination of a specific processingmethod, i.e., co-rotating twin screw technology and photo-inducedcrosslinking, which if combined with the novel chemical approachpresented in the present invention, produces crosslinked polyolefinicpipes that meets and exceeds the current standards applied for plasticpipes utilized for drinking water applications, such as crosslinkedpolyethylene (PEX).

A stabiliser package is typically needed to ensure the pipes havepractical utility. However, stabilisers also have a tendency to leachfrom plastics pipes over a period of time. Stabilisation ofthermoplastic polymers is usually accomplished by melt blending with oneor more stabilisers. In this way a heterophase polymer/stabiliser systemis formed, which may be best described as a physical dispersion of a lowmolecular weight stabiliser in a polymer matrix. The vast majority ofcommercial stabiliser compounds have very different chemical structurefrom that of the non-polar host thermoplastic polymer. For this reason,the compatibility of various conventional stabilisers with polyolefinsis generally poor, thereby leading to migration i.e. leaching of admixedstabilisers across the boundary of the polyolefin with neighbouringfluids, liquids, gases or solid materials. This loss of stabilisersubstantially shortens the lifetime of the polyolefin. Of more concernis the fact that the migration of stabilisers into drinking water(potable water) can also have unpredictable and potentially toxiceffects on consumers. We have previously developed a stabiliser packagethat is suitable for use in drinking water pipes, as is described in WO2010/138816.

A method for studying stabiliser migration involves immersing the pipein boiling water with subsequent measurement of the oxidation inductiontime (OIT) level, which gives an indication of how much activestabiliser is remaining in the pipe and measures how easily thestabiliser is able to leach out of the pipe wall.

Similarly, other additives such as crosslinking agents are required inorder to ensure the structural integrity of the pipes in the senses ofboth their immediate ability to withstand pressure from fluid beingtransported within, and to ensure their overall long-term performance.The long-term performance of plastics pipes is typically evaluated usingthe Standard Extrapolation Method (SEM) test of ISO 9080 (e.g. inEurope) or the ASTM D 2837 method (e.g. in North America). These methodsinvolve testing pipes that are pressurised at elevated temperatures andmeasures the time to burst at different stress levels. Considerableresearch effort has been focused on so-called stage III ruptures, whichtake place when the stabiliser package has ceased to be effective or ifthe degree of crosslinking is insufficient.

EP 0 490 854 B1 describes the use of double screw extruders incombination with UV irradiation to produce crosslinked polyethylenepipes such as those intended for hot water applications. This documentdiscloses specific photoinitiators for achieving crosslinking to enablethe fast processing of polymeric materials. A series of benzophenonederivatives is disclosed which are said to be compatible withpolyethylene. However, this document does not address the issue ofleaching of such materials from the polymer matrix.

The polymer materials of EP 0 490 854 B1 may be prepared using a twinscrew extruder. However, the patent is more concerned with the nature ofthe photoinitiators and does not actually describe the features of theextruder other than its ability to mix and extrude material. The linespeeds achievable with the process claimed in that patent are also quitelow and were in the range of 1 m/min or less. This is not ideal for acommercial process.

It is apparent that known extruded pipes and methods of making suchpipes are subject to a number of limitations. There is therefore a needfor new methods of production and/or new combinations of chemicalcomponents to improve the methods of production and/or properties ofpolyolefin pipes.

It is an aim of the present invention to provide materials for formingpipes that can be used in domestic cold and/or hot water application. Itis also an aim to provide materials for producing pipes for industrialapplication. It is an aim to produce pipes which are resistant to theleaching out over time of one or more of the additive components. Afurther aim is to produce pipes for domestic applications which meet orexceed current standards for one or more of burst strength, pressureresistance, degradation, leaching of additives over time,discolouration, and resistance to chlorine. The present inventionsatisfied some or all of these aims.

BRIEF SUMMARY OF THE DISCLOSURE

The present invention is concerned with a process for producing extrudedplastics pipes which benefit from a greatly reduced level of leaching ofchemical residuals relative to the existing products currently availablein the marketplace. The present invention also provides a pipe which isstable to leaching to a far greater degree than is the case forcurrently available pipes. The present invention also provides pipeswhich benefit from a greatly increased level of resistance to oxidativedegradation. The pipes show an excellent level of resistance to chlorineand exceed the current requirements for drinking water applications. Theprocess of the invention utilises a novel co-rotating twin-screwextrusion process which, as is described below, results in a producthaving substantially lower levels of leaching of chemical residualsrelative to existing extruded pipes used for drinking waterapplications. The new process also provides superior long-termperformance due to outstanding material mixing in the pipe extrusionprocess, leading to maximized pipe matrix homogeneity, which is criticalfor resistance to oxidation.

Preferably the present invention utilises combinations ofphotoinitiator(s) and co-agent(s), that can be combined in the processto provide the necessary level of crosslinking of the polyolefinicpolymer (e.g. polyethylene), to produce for example, PEX pipes. This isachieved at the same time as ensuring very low levels of leaching of thecomponents from the extended pipe. The present invention allows lowlevels of the various components to be used whilst still preservingexcellent properties in the finished pipe.

For NSF 61 requirements there is a need to choose the initiatorcarefully and to include a scavenger to provide low levels of leaching.Long term resistance to oxidative degradation may be of lesserimportance for such pipes of the invention.

Thus one aspect of the invention provides a polymeric pipe formed from apolyolefin structural polymer, a photoinitiator in an amount of 0.02 to3% by weight and a scavenger in an amount of 0.01 to 2% by weight,wherein the photoinitiator is a compound of formula I:

wherein

-   R¹ is selected from —(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)O(C═O)(CH₂)_(q)—,    —(C═O)(C₅-C₂₄ alkyl), and —(C═O)(C₅-C₂₄ alkenyl):-   R² is selected from —H, —OH, -halo, —(C₁-C₄)alkyl, —(C₂-C₄)alkenyl,    and formula II:

and

-   R³ is selected from —H, -halo, —OH, —(C₁-C₄)alkyl, —(C₂-C₄)alkenyl,    —O(C₁-C₄)alkyl, and —O(C₂-C₄)alkenyl;-   m is 0, 1 or 2; n is 2, 3, 4, 5, 6; p is 2-10; and q is 0, 1 or 2.    In an embodiment the photoinitiator is in an amount of 0.2 to 3% by    weight and the scavenger is in an amount of 0.1 to 2% by weight.

However, in other applications, long term stability to oxidativeresistance may be of benefit, for example in providing pipes withdesirable mechanical properties over extended periods. Such pipes of theinvention demonstrate improved long term stability when measured, forexample, in the ASTM F 876 Stabilizer Functionality Test. For such pipesleaching is less of an issue but it is essential to include aphotoinitiator, co-agent and antioxidant.

Thus another aspect of the invention provides a polymeric pipe formedfrom a polyolefin structural polymer, a photoinitiator in an amount of0.02 to 2% by weight, a co-agent in an amount of 0.02-10% by weight, andan antioxidant in an amount of 0.1 to 1.5% by weight; wherein thephotoinitiator is selected from benzophenone, benzophenone substitutedat the 4-position and benzophenone substituted at the 4 and 4′-position;and wherein the co-agent comprises at least one carbon-carbon doublebond. In an embodiment the photoinitiator is in an amount of 0.2 to 3%by weight and the co-agent is in an amount of 0.2-10% by weight.

Pipes of the invention may satisfy the NSF 61 requirements for lowlevels of leaching or long term stability chlorine resistancerequirement according to ASTM F2023. In addition, pipes of the inventionmay satisfy both NSF 61 requirements for low levels of leaching and longterm stability chlorine resistance requirement according to ASTM F2023.

We have found that the deliberate use of a twin extruder havingco-rotating twin screws provides the necessary conditions for extrudingplastics pipes which are more resistant to leaching of additives. Inaddition, the pipes of the invention demonstrate improved long termstability when measured, for example, in the ASTM F 876 StabilizerFunctionality Test. Furthermore, the process of the invention allows theproduction of PEX pipes at exceptionally high line speed relative toknown processes, under very efficient production conditions. Asdiscussed below, the process of the present invention can operate atline speeds of at least 20 m/min, for example in the range of 30-60m/min, whilst still producing stable robust extruded pipe, for examplefor a ½″ (1.27 cm) pipe as defined in the ASTM F876 standard for PEXtubing in North America.

Another aspect of the invention provides a method of producing across-linked polyolefin pipe comprising:

-   -   extrusion of a mixture from a co-rotating twin screw extruder to        form an extruded pipe; and    -   cross-linking a polyolefin structural polymer by irradiating the        extruded pipe with UV radiation,    -   wherein the extrusion mixture comprises the polyolefin        structural polymer, a photoinitiator in an amount of 0.02 to 3%        by weight and a scavenger in an amount of 0.01 to 2% by weight;    -   wherein the photoinitiator is a compound of formula I:

wherein:

-   R¹ is selected from —(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)(C═O)(CH₂)_(q)—,    —(C═O)(C₅-C₂₄ alkyl), and —(C═O)(C₅-C₂₄ alkenyl);-   R² is selected from —H, —OH, -halo, —(C₁-C₄)alkyl, —(C₂-C₄)alkenyl,    and formula II:

-   R³ is selected from —H, -halo, —OH, —(C₁-C₄)alkyl, —(C₂-C₄)alkenyl,    —C(C₁-C₄)alkyl, and —O(C₂-C₄)alkenyl;-   m is 0, 1 or 2; n is 2, 3, 4, 5, 6; p is 2-10; and q is 0, 1 or 2.    In an embodiment the photoinitiator is in an amount of 0.2 to 3% by    weight and the scavenger is in an amount of 0.1 to 2% by weight.

A further aspect of the invention provides a method of producing across-linked polyolefin pipe comprising:

-   -   extrusion of a mixture from a co-rotating twin screw extruder to        form an extruded pipe; and    -   cross-linking a polyolefin structural polymer by irradiating the        extruded pipe with UV radiation,    -   wherein the extrusion mixture comprises the polyolefin        structural polymer, a photoinitiator in an amount of 0.02 to 3%        by weight, a co-agent in an amount of 0.02-10% by weight, and a        phenolic antioxidant in an amount of 0.1 to 1% by weight;    -   wherein the photoinitiator is selected from benzophenone,        bezophenone substituted at the 4-position and benzophenone        substituted at the 4 and 4′-position; and    -   wherein the co-agent comprises at least one carbon-carbon double        bond. In an embodiment the photoinitiator is in an amount of 0.2        to 3% by weight and the co-agent is in an amount of 0.2-10% by        weight.

The pipes of the invention may be used to convey fluids, for exampledrinking water or hot water. Accordingly, another aspect of theinvention provides for the use of a pipe of the invention in a watertransport system. An embodiment provides the use of a pipe of theinvention in a drinking water transport system. Another embodimentprovides use of a pipe of the invention in a hot water transport system.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are further described hereinafter withreference to the accompanying drawings, in which:

FIG. 1 is a flowchart illustrating a process for making pipes of theinvention.

FIG. 2 is a line diagram illustrating apparatus that may be used toperform the process of steps 2 to 6 of FIG. 1.

FIG. 3 is a line diagram illustrating apparatus that may be used toperform the process of steps 7 to 9 of FIG. 1.

DETAILED DESCRIPTION

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to”, and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics, compounds, chemical moieties orgroups described in conjunction with a particular aspect, embodiment orexample of the invention are to be understood to be applicable to anyother aspect, embodiment or example described herein unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The invention is notrestricted to the details of any foregoing embodiments. The inventionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

For the avoidance of doubt, it is hereby stated that the informationdisclosed earlier in this specification under the heading “Background”is relevant to the invention and is to be read as part of the disclosureof the invention.

Polymeric pipes of this invention may be used for variety ofapplications, for example transport of hot and/or cold potable water,radiant floor heating, or waste water, as well as being used in firesprinklers, process pipes in industries such as the food industry, andfor conveying fluids other than water such as gases and slurries, amongother uses. In some embodiments, these polymeric pipes include a basepipe with one or more layers disposed on the base pipe. Examples ofvarious layers that may be disposed on a polymeric base pipe areincluded in US 2010/0084037, entitled “Methods and Compositions forCoating Pipe,” which is incorporated by reference in its entirety. Inother embodiments, the polymeric pipe includes the base pipe with nolayers disposed on the base pipe, i.e. the pipe will consist of a single(i.e. one) layer.

Pipe Standards and Certifications

Pipe standards and standard test procedures referenced in the presentdisclosure include the following:

-   ASTM International Standard for Crosslinked Polyethylene (PEX)    Tubing, F 876-10 (approved Feb. 1, 2010) (“ASTM F876”);-   ASTM International Standard Test Method for Evaluating the Oxidative    Resistance of Crosslinked Polyethylene (PEX) Tubing and Systems to    Hot Chlorinated Water, F2023-10 (approved Aug. 1, 2010) (“ASTM    F2023”);-   ASTM International Standard Test Method for Obtaining Hydrostatic    Design Basis for Thermoplastic Pipe Materials or Pressure Design    Basis for Thermoplastic Pipe Products D2837-11 (approved Apr.    1, 2011) (“ASTM D2837”);-   ASTM Standard Test Method for Oxidative-Induction Time of    Polyolefins by Differential Scanning calorimetry D 3859-98 (approved    Jul. 10, 1998) (“ASTM D3895”);-   NSF International Standard/American National Standard for Drinking    Water Additives 61-2011 (Jun. 10, 2011) (“NSF 61”); and-   EN ISO 15875.    The contents of all of these standards are incorporated herein by    reference.

The tests referred to herein are known standards in the industry and areavailable to the skilled person. We therefore only refer to them brieflyin the interests of brevity. However, the content of these standardsforms an integral part of the invention to the extent that the pipesaccording to the invention meet or exceed the requirements of thestandards. Hence the content of these standards is explicitlyincorporated into the present disclosure by reference.

Presently, PEX tubing in North America must meet temperature andpressure ratings requirements of 160 psi at 73.4° F. (23° C.), 100 psiat 180° F. (82.2° C.), and 80 psi at 200° F. (93.3° C.). Minimum burstratings are at 475 psi at 73.4° F. (⅝ inch and larger). Additionalperformance characteristics and requirements for PEX pipes and tubingare given in ASTM F867.

ASTM F876 (North America) and EN ISO 15875 (Europe): Before productlaunch, any pipes have to pass all required testing in accordance withthese two standards, respectively. The most time consuming and difficultrequirements are mentioned specifically below.

Temperature/Pressure Ratings: According to NSF/PPI, pipes are onlyapproved (for North America) if they pass 2,000 h of testing withoutdamage. This test is conducted at higher temperature and pressures.Generally a pipe should not fail if it passes this condition but thepipe still needs to pass 16,000 h for completion.

Chlorine resistance is measured by ASTM F2023 and requires approximately12-15 months of testing for completion.

A qualitative measure of the level of stabilisation may be provided bythe oxidative-induction time (OIT) test, as performed in accordance withASTM D3895.

Specific additives are typically needed for any application wherepolymers are utilized to create consumer products. For example, pipesfor drinking water applications typically comprise stabilizers,anti-oxidants, crosslinking agents, processing additives, etc. as partof the final pipe composition, regardless of manufacturing method. Theseadditives are typically necessary to provide pipes with desirablephysical properties, e.g. pipes that satisfy ASTM F876 and/or EN ISO15875 requirements. These chemical additives are, however, typicallysubject to leaching from the final chemical pipe. Leaching of chemicalsinto the pipe is, however, undesirable. In addition, for certainapplications there are limits set on levels of leached chemicals. Forexample, NSF 61 sets limits on chemical leaching for drinking waterpipes.

NSF 61 relates to the hygiene requirement and concerns the need tominimize chemical leaching from the finished pipes. Drinking water pipesin North America must pass the NSF 61 test. The purpose of this test isto assure the customer that the quality of the water inside the pipe isnot compromised by chemicals leaching into it. There are three ways tocomplete this test: 1) single point test, 2) 21-Day multipoint test and3) 107-Day multipoint test. All three tests involve changing the waterinside the pipe every 24 hours over an extended period of time. For thesingle point test only the water extract on Day 17 is tested. For themultipoint tests the water extracts on several days are analyzed and theresulting data is then used to create a decay curve.

The water extracts are analyzed by a Gas Chromatograph equipped with aMass Selective Detector (GC/MS). If deemed necessary other analyticaltechniques are also used. Twenty-four hours prior to collecting a samplefor analysis some of the samples are heated at 82° C. for 30 minutes.The heated extracts are then analyzed by GC/MS for semi-volatilecompounds using EPA624 method. The rest of the samples are conditionedat room temperature and then analyzed by GC/MS for volatile compoundsusing EPA524 method.

To pass the multipoint tests the concentration of all chemicalsextracted into the water must decay to below the Short Term ExposureLimit (STEL) on Day 17 and Total Allowable Concentration (TAC) on Day107. For the single point test both the STEL and TAC limits must be meton Day 17.

The allowance limits of NSF 61 were typically in the in the ppm rangeuntil recent years when the requirements have become more stringent, forexample with the limits set in the ppb range for a number of compoundsin current NSF standards.

The degree of crosslinking can be quantified in accordance with thefollowing citation from ASTM F876:

“6.8. Degree of Crosslinking—When tested in accordance with 7.9, thedegree of crosslinking for PEX tubing material shall be within the rangefrom 65 to 89% inclusive. Depending on the process used, the followingminimum percentages crosslinking values shall be achieved: 70% byperoxides (PEX-a), 65% by Azo compounds, 65% by electron beam (PEX-c),or 65% by silane compounds (PEX-b)”.Ideally, pipes should have a high, i.e. at least 50% (preferably atleast 65%), level of cross-linking according to the standard. However,in some applications a lower degree of cross-linking may be acceptable.

The present invention is able to produce extruded pipes thatconsistently satisfy a defined target level of crosslinking (CCL) of,for example 73%, and importantly we have found that we are able tomaintain it at that level at approximately 73±0.5% for a givenformulation. In conventional prior art extrusion processes thisvariation is at least 3% and up to 5%, but can be many times higher.

The present invention provides a process for producing pipes that mayhave a high CCL, i.e. a CCL of at least 65% (e.g. of at least 70%) in aconsistent and homogeneous manner, to satisfy or exceed the ASTM F876standard. Pipes of the invention may satisfy the NSF 61 standard forresiduals. Pipes of the invention may have a high CCL and also satisfythe NSF 61 standard for residuals.

Definitions

The following explanations of terms and methods are provided to betterdescribe the present disclosure and to guide those of ordinary skill inthe art in the practice of the present disclosure.

The terms “alkyl”, “C₁-C₁₀ alkyl” and “C_(x)-C_(y) alkyl” (where x is atleast 1 and less than 10, and y is a number greater than 10) as usedherein include reference to a straight or branched chain alkyl moietyhaving, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms. The termincludes reference to, for example, methyl, ethyl, propyl(n-propyl orisopropyl), butyl(n-butyl, sec-butyl or tert-butyl), pentyl, hexyl andthe like. In particular, alkyl may be a “C₁-C₆ alkyl”, i.e. an alkylhaving 1, 2, 3, 4, 5 or 6 carbon atoms; or a “C₁-C₄ alkyl”, i.e. analkyl having 1, 2, 3 or 4 carbon atoms. The term “lower alkyl” includesreference to alkyl groups having 1, 2, 3 or 4 carbon atoms.

The terms “alkenyl”, “C₂-C₁₀ alkenyl” and “C_(x)-C_(y) alkenyl” (where xis at least 2 and less than 10, and y is a number greater than 10) asused herein include reference to a straight or branched chain alkylmoiety having, e.g. 2, 3, 4, 5, 6, 7, 8, 9 or 10 carbon atoms andhaving, in addition, at least one double bond, of either E or Zstereochemistry where applicable. This term includes reference to, forexample, ethenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl,1-pentenyl, 2-pentenyl, 3-pentenyl, 1-hexenyl, 2-hexenyl and 3-hexenyland the like. In particular, alkenyl may be a “C₂-C₆ alkenyl”, i.e. analkenyl having 2, 3, 4, 5 or 6 carbon atoms; or a “C₂-C₄ alkenyl”, i.e.an alkenyl having 2, 3 or 4 carbon atoms. The term “lower alkenyl”includes reference to alkenyl groups having 2, 3 or 4 carbon atoms.

The term “cycloalkyl” as used herein includes reference to an alicyclicmoiety having 3, 4, 5, 6, 7 or 8 carbon atoms in a single ring. Thecycloalkyl may be functionalised with a group such as an epoxide toproduce a cycloalkyl epoxide. A group of this type will comprise twofused rings. The cycloalkyl may be functionalised with a group such asan isocyanate to produce a cycloalkyl isocyanate. Alternatively, thegroup may be a bridged or polycyclic ring system, more than one of whichmay be functionalised with epoxide. For example, a bridged or polycyclicring system may comprise two rings, both of which are functionalisedwith epoxide. More often cycloalkyl groups are monocyclic. The termcycloalkyl includes reference to groups such as cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, norbornyl, bicyclo[2.2.2]octyl and the like.

The terms “alkoxy” and “C₁-C₆ alkoxy” as used herein include referenceto —O-alkyl, wherein alkyl is straight or branched chain and comprises1, 2, 3, 4, 5 or 6 carbon atoms. In one class of embodiments, alkoxy has1, 2, 3 or 4 carbon atoms. This term includes reference to, for example,methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy, pentoxy,hexoxy and the like. The term “lower alkoxy” includes reference toalkoxy groups having 1, 2, 3 or 4 carbon atoms.

The terms “halo” or “halogen” as used herein includes reference to F,Cl, Br or I. In a particular class of embodiments, halogen is F or Cl,of which F is more common.

Where a compound, moiety, process or product is described as“optionally” having a feature, the disclosure includes such a compound,moiety, process or product having that feature and also such a compound,moiety, process or product not having that feature. Thus, when a moietyis described as “optionally substituted”, the disclosure comprises theunsubstituted moiety and the substituted moiety.

Where two or more moieties are described as being “independently” or“each independently” selected from a list of atoms or groups, this meansthat the moieties may be the same or different. The identity of eachmoiety is therefore independent of the identities of the one or moreother moieties.

The term “CCL” refers to the crosslink density, typically expressed as apercentage. Throughout the description and claims of this specification,the phrases “degree of crosslinking”, “level of crosslinking” and“crosslink density” or similar mean CCL.

Pipes

Unless indicated otherwise in this specification, any reference to aspecific component (e.g. polyolefin structural polymer, photoinitiator,reactive extrusion species, co-agent, hindered amine light stabiliser,antioxidant, or any optional additive) in an amount of % by weight is areference to the component as a % of its weight relative to the totalweight of the layer of the pipe in which it is present.

Polymeric pipes of the invention comprise a polyolefin structuralpolymer. Although the structural polymer may be polyethylene (PE), thoseof ordinary skill in the art understand that various other structuralpolymers may be used in place of polyethylene. For example, thestructural polymer may be a polyolefin such as PE (e.g., PE-raisedtemperature, or PE-RT), polypropylene (PP), polybutylenes (PB); anycopolymers thereof; polyolefin copolymers such aspoly(ethylene-co-maleic anhydride); among other polymers. For example,the structural polymer may be polyethylene, polypropylene, polybutylene,and higher olefinic polymers; copolymers of ethylene, propylene,1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene andisomers thereof with each other and with other unsaturated monomers.Block copolymers and polymer blends of polymerised monomers of any ofthe abovementioned polymers are also included. The polymeric pipe mayhave at least 85% by weight polyolefin structural polymer, at least 90%by weight polyolefin structural polymer, or at least 95% by weightpolyolefin structural polymer.

Preferred polyolefin structural polymers for use in the presentinvention include polyethylene, polypropylene, and mixtures thereof.

Polyethylene (PE) is classified into several different categories basedmostly on its density and branching. The final product performance andmechanical properties depend significantly on variables such as theextent and type of branching, the crystallinity, the density, and themolecular weight and its distribution. As mentioned, PEX pipes are byfar and most commonly manufactured from high density polyethylene(HDPE), however, this invention is applicable where any type ofpolyolefin or polyethylene is used for the production of single-layer ormulti-layer plastic pipes such as, but not limited to, low densitypolyethylene (LDPE), medium density polyethylene (MDPE), PE 100, PE 80,PE-RT grades, and ultra-high molecular weight polyethylene (UHMWPE) orcombinations thereof. Examples of commercially available PE that may beused in pipes of the present invention include Basell Q 456, Basell Q456B, Basell New Resin, Basell Q 471, (all three of which are availablefrom Equistar Chemicals, LP Lyondell Basell Company, Clinton Iowa,United States) Borealis HE 1878, Borealis HE 1878 E, Borealis HE 2550(all three of which are available from Borealis AG).

The polymeric pipes of the invention may comprise cross-linkedpolyethylene (PEX) as the polyolefin structural polymer, in which casethe pipe may be a PEX pipe. The structural polymer in such a pipe maycomprise or consist of any of the varieties of polyethylene mentionedherein which has been crosslinked, preferably by the action ofUV-radiation.

The pipes of the invention may be pipes, for example PEX pipes, thatmeet temperature and pressure ratings requirements of 160 psi at 23° C.(73.4° F.), 100 psi at 82.2° C. (180° F.), and 80 psi at 93.3° C. (200°F.). Minimum burst ratings are at 475 psi at 23° C. (73.4° F.) (⅝ inchand larger). PEX pipes of the invention may also meet additionalperformance characteristics and requirements set out in the ASTM F 876approved Feb. 1, 2010, which is incorporated by reference in itsentirety.

Polymeric pipes of the invention may comprise a photoinitiator, forexample one or more photoinitiators; e.g. at least 1, at least 2, atleast 3, at least 4 or at least 5 photoinitiators as defined herein. Thephotoinitiator may be present in an amount of 0.02 to 3% by weight, forexample 0.2 to 3% by weight, e.g. the photoinitiator may be present inan amount of 0.2 to 2.5% by weight or 0.2 to 2% by weight. For example,the photoinitiator may be present in an amount of 0.3 to 1.5% by weight,0.4 to 1.2% by weight, or 0.4 to 1% by weight; e.g. about 0.5% byweight, about 0.75% by weight or about 1% by weight.

The photoinitiator has an important role in crosslinking the polyolefinstructural polymer. The photoinitiator may be selected from the class of“Type II free radical Photoinitiators”. Exemplary Type IIphotoinitiators include benzophenone and its derivatives, thioxanthoneand its derivatives, anthraquinone and its derivatives, camphorquinone,benzyl, and dibenzosuberenone.

Type II photoinitiators undergo a bimolecular reaction where the excitedstate of the photoinitiator normally interacts with a second molecule(co-initiator) to generate free radicals. The excited state can alsoabstract hydrogens from the surrounding polymer matrix, e.g., from apolyethylene polymer backbone, to induce and complete the necessarycrosslinking, as being relevant in the present invention.

The photoinitiator may be benzophenone or a benzophenone derivative. Forexample, the photoinitiator may be selected from one or more ofbenzophenone, benzophenone substituted at the 4-position andbenzophenone substituted at the 4 and 4′-position. When such aphotoinitiator is used, the crosslinking process involves a radicalmechanism to facilitate crosslinking. This process is illustrated belowfor the photoinitiator benzophenone and PE and comprises the steps ofinitiation, hydrogen abstraction and crosslinking.

Initiation:

Hydrogen abstraction from the polyethylene chain:

Crosslinking to form a crosslinked polymer network (in this examplePEX):

The photoinitiator may be a benzophenone substituted at the 4-positionor 4 and 4′-position of the following formula:

R¹⁵ is selected from the group comprising —H, -halo, —OH,—(C₁-C₁₀)alkyl, —(C₂-C₁₀)alkenyl, —O(C₁-C₁₀)alkyl, and—O(C₂-C₁₀)alkenyl.

In an embodiment, R¹⁵ is selected from the group comprising —H, -halo,—OH, —(C₁-C₄)alkyl, —(C₂-C₄)alkenyl, —O(C₁-C₄)alkyl, and—O(C₂-C₄)alkenyl. R¹⁵ may be selected from -halo (e.g. —F or —Cl),—(C₁-C₄)alkyl (e.g. -methyl or -ethyl), and —O(C₁-C₄)alkyl (e.g.-methoxy or -ethoxy). R¹⁵ may be H, in which case the benzophenone isnot substituted at the 4′-position, i.e. the photoinitiator is abenzophenone substituted at the 4-position.

R¹⁶ is selected from the group comprising -halo, —OH, —(C₁-C₃₀)alkyl,—(C₂-C₃₀)alkenyl, —O(C₁-C₃₀)alkyl, —O(C₂-C₃₀)alkenyl,—O(C═O)(C₁-C₃₀)alkyl, —O(C═O)(C₂-C₃₀)alkenyl, and —O—R¹—R².

In an embodiment, R¹⁶ is selected from the group comprising -halo, —OH,—(C₁-C₂₀)alkyl, —(C₂-C₂₀)alkenyl, —O(C₁-C₂₀)alkyl, —O(C₂-C₂₀)alkenyl,—O(C═O)(C₁-C₂₀)alkyl, —O(C═O)(C₂-C₂₀)alkenyl and —O—R¹—R². For example,R¹⁶ may be selected from —(C₁-C₁₀)alkyl, —(C₂-C₁₀)alkenyl,—O(C₁-C₁₀)alkyl, —O(C₂-C₁₀)alkenyl and —O—R¹—R².

R¹ is selected from the group comprising—(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)(C═O)(CH₂)_(q)—, —(C═O)(C₅-C₂₄ alkyl),and —(C═O)(C₅-C₂₄ alkenyl).

In an embodiment, R¹ is selected from the group comprising—(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)(C═O)(CH₂)_(q)— or —(C═O)(C₅-C₂₄ alkyl).R¹ may be —(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)(C═O)(CH₂)_(q)—, R¹ may be—(C═O)(C₅-C₂₄ alkyl).

R² is selected from the group comprising —H, —OH, -halo, —(C₁-C₄)alkyl,—(C₂-C₄)alkenyl, and formula II:

R² may be selected from —H, -halo, —(C₁-C₄)alkyl and formula II. Forexample, R² may be —H or of formula II. For example, R² may be H.

In an embodiment, R² may be of formula II.

R³ is selected from the group comprising —H, -halo, —OH, —(C₁-C₄)alkyl,—(C₂-C₄)alkenyl, —O(C₁-C₄)alkyl, and —O(C₂-C₄)alkenyl.

R³ may be selected from —H, -halo, and —OH. R³ may be —H.

In an embodiment, R³ may be —(C₁-C₄)alkyl. For example, R³ may be—O(C₁-C₄)alkyl.

m is 0, 1 or 2. Preferably, m is 0 or 1.

n is 2, 3, 4, 5, 6. Preferably, n is 3, 4 or 5.

p is 2-10. Preferably, p is 4, 5, 6, 7 or 8.

q is 0, 1 or 2. Preferably, q is 0 or 1.

For example, m and q may both be 1 and/or m and q may both be 0. Forexample, n may be 3, 4 or 5 (e.g. 4) and p may be 3, 4, 5 or 6.

The photoinitiator may thus be a compound of formula I:

R¹, R², and R³ are as previously defined.

Examplary benzophenones of use in the present invention are disclosed inEP0490854 A2, which is specifically incorporated by reference in itsentirety and the initiators used in that document are intended to formpart of this invention.

Oligomeric/polymeric benzophenones are preferred, as these may result inless leaching of photoinitiator residues into fluid contained within thepipe.

The photoinitiator may be a compound selected from benzophenone,4-hydroxybenzophenone laurate, 4-hydroxybenzophenone stearate,4-chloro-4′-hydroxybenzophenone laurate, 4-chloro-4′-hydroxybenzophenonestearate, 4,4′-dimethylbenzophenone, 4,4′-dimethoxybenzophenone,4-chlorobenzophenone, 4-fluorobenzophenone,4-fluoro-4′-hydroxybenzophenone, 4,4′-diallyloxybenzophenone, OmnipolBP, and Genopol BP. Omnipol BP is the compound:

Genopol BP is the compound:

For example, when the photoinitiator is Omnipol BP a satisfactorycrosslinking value is obtained for the polyolefin polymer and we canmeet the NSF 61 requirement for residuals, e.g. when used in a pipe ofthe invention comprising a scavenger.

Polymeric pipes of the invention may comprise a scavenger, for exampleone or more scavengers; e.g. at least 1, at least 2, at least 3, atleast 4 or at least 5 scavengers as defined herein. The scavenger may bea reactive extrusion species or nanoparticles, or a mixture of two ormore reactive extrusion species and/or nanoparticles. The reactiveextrusion species may be a mono- or multi-functional isocyanate (e.g. analkyl isocyanate, aryl isocyanate, cycloalkyl isocyanate, oligomericisocyanate, and/or polymeric isocyanate), or it may be an epoxide ormixture thereof. The scavenger (or total amount of scavengers) may bepresent in an amount of 0.01 to 5% by weight. For example, the scavengermay be present in an amount of 0.2 to 1% by weight, 0.3 to 0.7% byweight, e.g. about 0.5% by weight.

Without being bound by any theory, it is thought that migration andleaching of any residues of the photoinitiator remaining aftercrosslinking from the polymeric pipe is substantially reduced byinteraction with the scavenger. Where the scavenger is a reactiveextrusion species, the interaction is based on a reaction. For example,where the reactive extrusion species is an alkyl isocyanate, the alkylisocyanate is able to react with a hydroxyl group of a photoinitiator ora hydroxyl group residue of a photoinitiator to form a covalent linkage.For example, an alkyl isocyanate would react with hydroxybenzophenone toform a urethane linkage between the alkyl group of the isocyanate andthe benzophenone. Similarly, when the reactive extrusion species is anepoxide (e.g. a cycloalkyl epoxide) the epoxy moiety may react with anappropriate substituent of the photoinitiator (or residue of thephotoinitiator) to form a covalent linkage.

Without wishing to be bound by any theory, it is believed that the alkylor cycloaliphatic groups of the reactive extrusion species contribute toreduced leaching from the polymer matrix of the residues after reactionto form a covalent linkage. For example, it is believed that the alkylor cycloaliphatic groups of the reactive extrusion species provide aportion of the compound that is compatible with a polyolefin structuralpolymer (e.g. a polyethylene). This compatibility provides a level ofmiscibility and homogeneity in the polymer blend that prevents theleaching of the reactive extrusion species and any bound residues out ofthe pipe.

The reactive extrusion species may comprise (or be) an alkyl isocyanate,cycloalkyl isocyanate, an oligomeric isocyanate, and/or polymericisocyanate. An alkyl isocyanate or cycloalkyl isocyanate may be amonofunctional or multi-functional isocyanate, e.g. may be adiisocyanate. The isocyanate may comprise an alkyl isocyanate, e.g.(C₆-C₃₀ alkyl)NCO or e.g. OCN(C₆-C₃₀ alkyl)NCO. The alkyl may be astraight chain or branched. The alkyl isocyanate may be a C₁₂, C₁₃, C₁₃,C₁₄, C₁₅, C₁₆, C₁₇, C₁₈, C₁₉, C₂₀, C₂₁ or C₂₂ alkylisocyanate, e.g.octadecylisocyanate. The isocyanate may comprise a cycloalkylisocyanate, for example isophorone diisocyanate. The isocyanate maycomprise a polymeric isocyanate, e.g. a polymeric isocyanate based onhexamethylene diisocyanate and/or isophorone diisocyanate. Mixtures ofisocyanates may be used in the present invention. Exemplary isocyanatesinclude octadecyl isocyanate, trans-cyclohexane diisocyanate (e.g.available from DuPont), Krasol NN32 (9% NCO, MDI based, available fromCray Valley, Exton, Pa., USA); and Desmodur polyisocyanates availablefrom Bayer Material Science (e.g. Desmodur W, BL 3175A, 4265 SN, DA-L,DN, HL BA, I, N 100, N 3200, N 3300A, N 3400, N 3600, XP 2617 and H).

Examples of isocyanates useful in the present invention are methylenediphenyl diisocyanate (MDI); Desmodur® W (hydrogenated MDI); monomerictoluene diisocyanate (TDI) based derivatives such as Desmodur® T65N,Desmodur® T80, Desmodur® T100; and L 67 MPA/X, L 67 BA (isocyanurate), L1470 (isocyanurate), IL BA (isocyanurate), IL EA (isocyanurate), IL 1351(isocyanurate), IL 1351 EA (isocyanurate), IL 1451 (isocyanurate), IL1451 EA (isocyanurate), HL BA (isocyanurate), HL EA (isocyanurate); andprepolymers based on TDI such as Desmodur® E 15, Desmodur® E 14,Desmodur® E 1361 MPA/X, Desmodur® E 1361 BA, Desmodur® E 1160, Desmodur®E 1750 PR, Desmodur® E 1660, Desmodur® E XP 2606; and monomericdiphenylmethane diisocyanate (MDI) products such as Desmodur® 44M,Desmodur® 44MC, Desmodur® 44MN, Desmodur® LS2424, Desmodur® 2460M,Desmodur® CD-S, Desmodur® CD-L, and polymeric MDI products such asDesmodur® VK5, Desmodur® VK10, Desmodur® VK10L, Desmodur® VLR10,Desmodur® VKS20, Desmodur® VKS20F, Desmodur® VKS20FH, Desmodur® XP2404,Desmodur® 44V70L; and Desmodur polymeric MDI products such as VL, VL50,VL51, VLR10, VLR20, VLR21, XP2551; and prepolymers based on MDI such asDesmodur® VH20N, Desmodur® E29, Desmodur® PF, Desmodur® EXP2753,Desmodur® E21, Desmodur® XP2665, Desmodur® E20100, Desmodur® EXP2723,Desmodur® E23, Desmodur® EXP2727, Desmodur® EXP2715, Desmodur® E2200176,Desmodur® E22, Desmodur® EXP2726, Desmodur® M280, AND Desmodur®VPLS2397; and aliphatic isocyanates such as Desmodur® H, Desmodur® I,Desmodur® W/1; and Desmodur® N-HDI-BASED-BIURET isocyanates such asN100, N75MPA/X, N75MPA, N75BA, N3200; and Desmodur® N-HDI-BASED-TRIMERisocyanates such as N3300, N3390BA/SN, N3390BA, N3600, N3790BA, N3800,N3900, XP2675, XP2580, N3400, XP2730, XP2679, XP2714; and Desmodur®Z-IPDI-BASED-BIURET isocyanates such as Z4470SN, Z4470MPA/X, Z4470BA,XP2565, XP2489, NZ1; and pre-polymers based on aliphatic isocyanatessuch as Desmodur® EXP2747, Desmodur® E305, Desmodur® XP2617, Desmodur®XP2599, Desmodur® E3265MPA/SN, Desmodur® E3370, Desmodur® VPLS2371,Desmodur® XP2406; and BAYHYDUR polyisocyanates such as 3100, 304, 305,401-70, XP2451, XP2487/1, XP2547, XP2655, XP2700, XP2759; and Desmodur®D based polyisocyanates such as DA-L and DN; and Desmodur® R materialssuch as RC, RN, RE, RFE; and Desmodur® BL blocked polyisocyanates suchBL1100/1, BL1265MPA/X, BL3175SN, BL4265SN, BL5375, BL3575/1, PL350,PL340, BL3370MPA, BL3475BA/SN, BL3272MPA, VPLS2078/2, Desmocap® 11,Desmocap® 1190, Desmocap® 12, BL5140, BL2805XP, BL5335, VPLS2310,BL2781XP, BLXP2706, BL2810XP; and BAYTHERM resins such as 3146, 2782XP;and Crelan® blocked isocyanates such as EF403, UI, NI-2, VPLS2256, andNW-5; all of which are available from Bayer Materials Science. Examplesof further isocyanates useful in the present invention are Rubinate M,Rubinate 5025, Rubinate 1245, Rubinate 1820, Rubinate 9016, Rubinate9257, Rubinate 44, Rubinate 1680, Rubinate 9447, Rubinate 9480, Rubinate9495, Rubinate 9009, Rubinate 9259, Rubinate 9041, Rubinate 9236,Rubinate 9040, Rubinate 9272, Rubinate 9511, Rubinate 9234, Rubinate9271, Rubinate 1790, Rubinate 1670, Rubinate 1209, Rubinate 9465,Rubinate 1234; Suprasec 5025, Suprasec 9615, Suprasec 9582, Suprasec9602, Suprasec 2004, Suprasec 9150, Suprasec 9561, Suprasec 9603,Suprasec 9608, Suprasec 9616, Suprasec 9611, Suprasec 9584, Suprasec9610, Suprasec 2496, Suprasec 9600, Suprasec 9577, Suprasec 2029,Suprasec 7316, Suprasec 7507, and Suprasec 9612; all of which areavailable from Huntsman Corporation, Michigan, USA.

The reactive extrusion species may comprise (or be) an epoxide oranother cyclic ether derivative (e.g. an oxetane); for example acycloalkyl epoxide or a cycloalkyl ether derivative (e.g. a cycloalkyloxetane). Illustrative of the cycloaliphatic epoxides useful as in thepresent invention are 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, bis-(3,4-epoxycyclohexyl)adipate, methyl3,4-epoxy-cyclohexane-carboxylate, ethyl3,4-epoxycyclohexane-carboxylate, propyl3,4-epoxycyclohexane-carboxylate, isopropyl3,4-epoxycyclohexane-carboxylate, n-butyl-, s-butyl-, and t-butyl3,4-epoxycyclohexane-carboxylate; the various amyl and hexyl3,4-epoxycyclohexane-carboxylates, methyl 3,4-epoxy-3-methyl-cyclohexanecarboxylate, ethyl 3,4-epoxy-3-methyl-cyclohexane carboxylate, methyl3,4-epoxy-4-methyl-cyclohexane carboxylate, ethyl3,4-epoxy-4-methyl-cyclohexane carboxylate, butyl3,4-epoxy-3-methyl-cyclohexane carboxylate, butyl3,4-epoxy-4-methyl-cyclohexane carboxylate, methyl3,4-epoxy-6-methyl-cyclohexane carboxylate, ethyl3,4-epoxy-6-methyl-cyclohexane carboxylate, butyl3,4-epoxy-6-methyl-cyclohexane carboxylate, dialkyl4,5-epoxycyclo-hexane-1,2-dicarboxylates, as well mixed dialkyl4,5-epoxycyclohexane-1,2-dicarboxylates, and the like. Mixtures ofcycloaliphatic epoxides and/or cyclic ethers can be employed. Anotherepoxide that may be used as a reactive extrusion species is allylglycidyl ether.

The scavenger may comprise (or be) nanoparticles, for example inorganicnanoparticles. Nanoparticles are defined as materials having onedimension below 200 nm. Without being bound by any theory, it isbelieved that nanoparticles may act to adsorb residues of thephotoinitiator or other polar components, thereby leading to reducedleaching of photoinitiator residues from the polymer matrix into anyfluid (for example water) that is resident in the pipe. The improvedresults obtained using nanoparticles may be due in part to theirextremely high aspect ratio compared to conventional fillers.

Especially suitable nanoparticles can be derived from inorganicmaterials, for example, nano-clays (e.g. intercalated and exfoliated(delaminated) clays (layered silicates)), calcium carbonate, calciumphosphate, aluminium oxide, silicon carbide SiC (nanowhiskers) andsilica SiO₂. Preferably at least 50% of the nanoparticles are less thanabout 20 layers thick, the layers of the nanoparticles having a unitthickness of from about 0.7 nm to 1.2 nm.

The nanoparticles may be layered silicates. Polymer-layered silicatecomposites can be divided into three general types: composites where thelayered silicate acts as a normal filler, intercalated nanocompositesconsisting of a regular insertion of the polymer material in between thesilicate layers and exfoliated nanocomposites where 1 nm-thick layersare dispersed in the polymer material forming a monolithic structure onthe microscale. All three types can be used in the pipes of the presentinvention. Layered silicates are believed to be especially beneficial inpolymer compositions in accordance with the invention due to their largesurface area in comparison with some other nanoparticles.

Any suitable layered silicate nanoparticles may be used as nanoparticlesin the plastics pipe of the invention. In this specification, the term“layered silicates” includes natural clays and minerals, for example,montmorillonite and talc, and also synthesized layered silicates such asmagadiite, mica, laponite, and fluorohectorite. These layered silicatesmay be subjected to various surface treatments with organic wetting orcoating agents as appropriate to introduce pendant polar groups.Mixtures of different layered silicates, and mixtures of layeredsilicates with other nanoparticles, may also be used.

Examples of suitable nanoparticles include montmorillonites, such asCloisite 6A and Cloisite 15A (sodium montmorillonite modified with aquaternary ammonium salt) manufactured by Southern Clay Products.Further examples of suitable nanoparticles include aluminium oxideparticles and/or a nanoclay such Nanomer 1.31 PS, surface modifiednanoclay (Aldrich product No. 682632, available from Sigma-Aldrich,St-Louis, Mo., USA on Jan. 4, 2013).

Polymeric pipes of the invention may comprise a co-agent, for exampleone or more co-agents; e.g. at least 1, at least 2, at least 3, at least4 or at least 5 co-agents as defined herein. The selected co-agents(monomers and/or oligomers) used in the formulations in the presentinvention comprise at least one polymerizable double bond or reactivegroup. The co-agent provides additional crosslinks between thepolyolefin chains of the polyolefin structural polymer. The co-agentthus acts to promote and enhance the efficiency of the crosslinkingprocess, e.g. where the polyolefin structural polymer is polyethylenethe co-agent enhances the crosslinking of the polyethylene chains toproduce PEX. The co-agent (or total amount of co-agents) may be presentin an amount of 0.02 to 10% by weight. For example, the co-agent may bepresent in an amount of 0.1 to 5% by weight, 0.2 to 1% by weight, 0.3 to0.7% by weight, e.g. about 0.5% by weight.

The co-agent may be selected from co-agents comprising reactive groupssuch as acrylates, allyl ethers, polybutadienes, vinyl ethers, and alsounsaturated vegetable oils, such as soybean oil. For example, theco-agent may be selected from acrylates, allyl ethers, polybutadienesand vinyl ethers. The co-agent may comprise a reactive carbon-carbondouble bond. A reactive carbon-carbon double bond may be a carbon-carbondouble bond that is a terminal carbon-carbon bond. A reactivecarbon-carbon double bond may be a carbon-carbon double bond where oneof the carbon atoms comprises two geminal hydrogen atoms.

The co-agent may comprise multiple double bonds. We have discovered thatthis enhances the level of crosslinking. Preferred co-agents comply withNSF 61 requirements. Polymeric co-agents such as polybutadienes, or anypolymer backbone containing unsaturated moieties may be used within theframework of the present invention, and will typically comply with NSF61 requirements when used in pipes of the invention.

For example, a wide variety of acrylates can be used as co-agents, andinclude: 1,6-hexanediol diacrylate, 1,3-bytylene glycol diacrylate,diethylene glycol diacrylate, trimethylolpropane triacrylate, neopentylglycol diacrylate, polyethylene glycol 200 diacrylate, tetraethyleneglycol diacrylate, triethylene diacrylate, pentaerythritoltetraacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol-Adiacrylate, propylene glycol (mono)dimethacrylate, trimethylolpropanediacrylate, di-trimethylolpropane tetraacrylate, triacrylate oftris(hydroxyethyl) isocyanurate, dipentaerythritol hydroxypentaacrylate,pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate,triethylene glycol dimethacrylate, ethylene glycol dimethacrylate,tetraethylene glycol dimethacrylate, polyethylene glycol-200dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycoldimethacrylate, polyethylene glycol-600 dimethacrylate, 1,3-butyleneglycol dimethacrylate, ethoxylated bisphenol-A dimethacrylate,trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate,diethylene glycol dimethacrylate, pentaerythritol tetramethacrylate,glycerin dimethacrylate, trimethylolpropane dimethacrylate,pentaerythritol trimethacrylate, pentaerythritol dimethacrylate,pentaerythritol diacrylate, aminoplast(meth)acrylates, acrylated oilssuch as linseed, soy bean oil, castor oil, etc. Other applicablepolymerizable compounds include methacrylamides, maleimides, vinylacetate, vinyl caprolactam, thiols and polythiols. Styrene derivativesare also readily applicable within the framework of this invention.

The co-agent may be an oligomer or a pre-polymer. For example, theco-agent may be an oligomer or a pre-polymer having acrylatefunctionality, e.g. selected from polyurethane acrylates, epoxyacrylates, silicone acrylates, and polyester acrylates. Other exemplaryco-agents include (meth)acrylated epoxies, (meth)acrylated polyesters,(meth)-acrylated silicones, (meth)acrylated urethanes/polyurethanes,(meth)acrylated polybutadiene, (meth)acrylated acrylic oligomers andpolymers, and the like, and any combinations thereof. A preferredco-agent is an oligomer or pre-polymer that is a polyurethane acrylate,for example a Krasol NN prepolymer (available from Cray Valley, Inc.,Exton, Pa., USA).

For example, we used polybutadiene-Ricon 152 and obtained a CCL value of80% and a pass for the NSF 61 test and a clear pipe in terms of colour.Similarly we used trimethylolpropane triacrylate (TMPTA) and obtained anacceptable CCL value and a pass for the NSF 61 test and a clear pipe interms of colour.

Further examples of co-agents of use in the invention include thefollowing:

Triallylcyanurate

Polybutadiene

wherein n is selected such that the average molecular weight is fromabout 2,000 to about 10,000 g/mol, preferably from about 4,000 to about7,000 g/mol, e.g. the average molecular weight may be 3,000 or 5,000g/mol.

Hydroxy terminated and epoxidized polybutadiene (Poly BD 600E)

having an average molecular weight of about 2,100 g/mol.

Polybutadiene-Ricon

wherein x and y are selected such that the average molecular weight isfrom about 1,000 to about 10,000 g/mol, preferably from about 2,000 toabout 7,000 g/mol. For example, Polybutadiene-Ricon 142 of averagemolecular weight 4,100 g/mol (CAS #9003-17-2). Polybutadiene-Ricon 152of average molecular weight 2,900 g/mol (CAS #9003-17-2).Polybutadiene-Ricon 156 of average molecular weight 2,900 g/mol.Polybutadiene-Ricon 157 of average molecular weight 1,800 g/mol.

Trimethylolpropane triacrylate (TMPTA)

Poly(ethylene glycol)diacrylate (CAS #: 26570-48-9)

where n is selected such that the average molecular weight is about 575g/mol.

Polybutadiene diacrylate (CAS #: 9003-17-2) of average molecular weight2,200 g/mol.

Krasol® NN polyurethane prepolymer (available from Cray Valley, Inc.,Exton, Pa., USA), for example Krasol® NN 32 (9% NCO, MDI based, 56%vinyl content, viscosity of 12,000 Cps at 25° C. and/or Krasol® NN 35.

Polymeric pipes of the invention may comprise a hindered amine lightstabilizer (HALS), for example one or more HALS; e.g. at least 1, atleast 2, at least 3, at least 4 or at least 5 HALS as defined herein.HALS are compounds in which an amine group is sterically hindered byadjacent functional groups. The physical properties of structuralpolymers such as PE may tend to degrade over time when exposed toultraviolet (UV) wavelengths of light. The use of HALS in the polymerblend interferes with this degradation and facilitates the maintenanceof the structural polymer properties over time. The total amount of HALS(e.g., any one or more of the HALS described herein) may be from 0.05 to1% by weight, from 0.05 to 0.5% by weight, from 0.07 to 0.3% by weight,from 0.1 to 0.25% by weight, or from 0.1 to 0.2% by weight; or about0.1% by weight, or about 0.15% by weight.

Exemplary HALS are described in WO 2010/138816 A1, which is incorporatedby reference in its entirety. For example, WO 2010/138816 A1 discloses,at paragraph [0050] on pages 15 to 17, HALS that may be used in thepipes of the invention.

The HALS may comprise a piperidine group. In some such embodiments, theHALS may be a compound of the following formula:

Each R⁷ and R⁸ may be hydrogen or a C₁-C₃₀ saturated or unsaturatedaliphatic moiety. R⁹ may be a C₂-C₃₀ saturated or unsaturated straight,branched or cyclic aliphatic moiety such as a hydrocarbon (consistingonly of carbon and hydrogen), an ester, an ether, or other suitablefunctional group.

In some embodiments, at least one of the R⁷ groups at each of the 2 and6 positions is a C₁-C₃₀ saturated or unsaturated straight, branched orcyclic aliphatic moiety, while in other embodiments both of the R⁷groups at each of the 2 and 6 positions is a C₁-C₃₀ saturated orunsaturated straight, branched or cyclic aliphatic moiety. In oneexample, one or both of the R⁷ groups at the 2 and 6 positions in thepiperidine ring are alkyl groups (e.g., a methyl or ethyl group), and R⁸is a hydrogen, methyl or ethyl group.

R⁹ may be a long chain (C₆ or greater, C₈ or greater, C₁₂ or greater, orC₁₆ or greater) straight or branched aliphatic functional group, atleast a portion of which is compatible with a nonpolar polyolefinstructural polymer such as PE. R⁹ may include an alicyclic structuresuch as a second piperidine ring. Where R⁹ includes a piperidine ring, aportion of R⁹ may act as a bridge between two piperidine rings. In somesuch embodiments, the bridge between the two piperidine rings may be asaturated aliphatic moiety or an unsaturated aliphatic moiety (e.g., itmay contain a C—C double bond such as methylene). In addition, R⁹ mayalso be included at other positions on the piperidine ring, for exampleat any one, any two, or at all three of, the 3, 4 and 5 positions on thepiperidine ring.

R⁹ may be an ester of formula —R¹⁰C(O)OR¹¹ or —R¹¹C(O)OR¹⁰ may beeither) the piperidine ring (where the ester moiety is attached directlyto the piperidine ring) or an additional functional group (e.g., aC₁-C₃₀ saturated or unsaturated aliphatic functional group) thatfunctions as a bridging group between the ester moiety and thepiperidine ring. R¹¹ may be a C₂-C₃₀ saturated or unsaturatedcarbon-containing moiety, for example an aliphatic function group (e.g.,a straight, branched or cyclic aliphatic group). R¹¹ together with thecarbon atom of the ester moiety may form a C₂-C₃₀ saturated orunsaturated ester.

Further examples of HALS of use in the present invention are thefollowing:

Cyasorb 3853, which may represented by formula

which has a molecular weight of 379 g/mol.

Chimassorb 944LD, which may be represented by formula

which has a molecular weight of 2000 to 3100 g/mol.

Tinuvin 770, which may be represented by formula

which has a molecular weight of 481 g/mol.

Tinuvin 622, which may be represented by formula

which has a molecular weight of 3100 to 4000 g/mol.

Without being bound by any theory, it is believed that the structure ofthe HALS of the invention contributes to reduced leaching from thepolymer matrix. For example, it is believed that the relatively longchain fatty acid portions that do not act as bridging groups in the HALSCyasorb 3853 provide a portion of the compound that is compatible with apolyolefin structural polymer (e.g. a polyethylene). This compatibilityprovides a level of miscibility and homogeneity in the polymer blendthat both improves the burst strength of the finished pipe and preventsand/or reduces the leaching of the Cyasorb 3853 into any water that isresident within the pipe.

Polymeric pipes of the invention may comprise an antioxidant, forexample one or more phenolic antioxidants; e.g. at least 1, at least 2,at least 3, at least 4 or at least 5 antioxidants as defined herein.Antioxidants may be used to preserve the polymer blend during theproduction process, for example when the polymer blend is exposed to theelevated heat and pressure of the extrusion process. Specifically, themechanical properties of some structural polymers, such as PE, will tendto deteriorate due to oxidative degradation when exposed to heat andpressure. For example, in some cases the deterioration will evidence asthe formation of shorter chains, effectively decreasing the averagemolecular weight of the structural polymer and changing thecharacteristics of the structural polymer. Antioxidants act to preventor limit such deterioration.

Antioxidants may also facilitate the maintenance of pipe properties overtime, especially when the pipe is exposed to chlorine or other oxidizingagents. In one example, a fluid (e.g. potable water) that is present inthe pipe may contain oxidizing agents such as chlorine, which over timemay tend to oxidize and break down a structural polymer such as PE. Suchoxidation may cause degradation in the properties of the structuralpolymer and the finished pipe. In some examples, antioxidants tend topreserve the properties of the structural polymer in the presence of anoxidative environment. The total amount of antioxidant (e.g., any one ormore of the antioxidants described herein) may be from 0.1 to 1% byweight, from 0.25 to 0.75% by weight, from 0.2 to 0.6% by weight, from0.38 to 0.57% by weight, or about 0.5 wt %.

Suitable antioxidants include phenolic antioxidants. Examples of suchantioxidants are described in WO 2010/138816 A1, which is incorporatedby reference in its entirety. For example, WO 2010/138816 A1 discloses,at paragraph [0048] on pages 12 to 14, antioxidants that may be used inthe pipes of the invention. Exemplary antioxidants that may be used inthe polymeric pipes of the invention include:

Certain pipes of the invention that comprise a hindered amine lightstabilizer and/or an antioxidant may provide an oxidative resistance asmeasured under the OR test (described under the subheading “Assays”below) of greater than 50 years, greater than 75 years, greater than 100years, greater than 150 years, or greater than 200 years. CertainAO/HALS combinations may also provide greater than 60 minutes, greaterthan 75 minutes, greater than 90 minutes, greater than 100 minutes, orgreater than 125 minutes under the OIT test.

Pipes of the invention may comprise further additives, for example thepipes may comprise processing aids, e.g. fluoropolymers. For example,pipes of the present invention may comprise a fluoropolymer that isselected from 3M™ Dynamar™ polymer processing additives, e.g. 3M™Dynamar™ Polymer Processing Additive FX 9613 (available from 3M Center,St. Paul, Minn.). When the pipe comprises at least one processing aid,the processing aid may be present at a level of from 0.01 to 1% byweight, for example 0.01 to 0.5% by weight; e.g. 0.02 to 0.4% by weight,0.02 to 0.1% by weight.

In a preferred embodiment, the material compositions for the pipesaccording to the invention include combinations of a least one componentselected from each of the following six classes of chemical compounds(and may include more than one component from one or more classes):polyolefin, most preferably polyethylene; photoinitiator(s); co-agent(s)(monomers and/or unsaturated oligomers and/or unsaturated polymers);anti-oxidant(s); and processing aids. In the case of drinking waterpipes, the required components further include light stabilisers, suchas hindered amine light stabilizer(s); and scavengers(s). All of thesecomponents may be as defined previously.

Methods

Pipes may be manufactured in accordance with a method or process of theinvention. The process of the present invention specifically requiresboth a co-rotating twin screw extruder to produce PEX pipes and thepresence of at least one UV irradiator unit to achieve the crosslinking.The process may include a gear pump to ensure consistency of theextrudate. The process is based on photo-induced crosslinking (UVirradiation) which is very fast and has flexibility in material choice.However there is no premature crosslinking in the extruder.

Specific details of the apparatus of the invention can be seen from theflowchart of FIG. 1 and the schematic drawing in FIG. 2 and FIG. 3. Theapparatus of the invention is typically arrange “in line” as a singleproduction line, for example to provide greater convenience. For thepurposes of providing enhanced clarity in the schematic drawings,however, the apparatus has been split over FIG. 2 and FIG. 3. Withreference to FIGS. 1 to 3, the apparatus typically includes thefollowing components:

(A) Batch mixing: polyolefin structural polymer (e.g. HDPE), along withphotoinitiator(s); and optionally one or more of an anti-oxidant (AO), alight stabiliser such as a hindered amine light stabilizer (HALS),co-agent(s) and processing aid(s), to make up the formulation. When ascavenger is used, the scavenger may also be included in theformulation. These components may be premixed in a rotational mixer. Thecomponents may be the components of a pipe of the invention as describedherein.

(B) Feeding: The mixed material is metered into the extrusion feedthroat 2.

(C) Co-rotating twin screw extrusion: A co-rotating twin screw extruder3 is used to melt, mix, and meter material. With co-rotating, modularscrew design technology, influence on material processing properties canbe achieved by altering the screw configuration. Influence on materialprocessing properties can also be achieved separately by running atvariable RPM, and/or by changing individual barrel temperature values.High flexibility in output and line speeds are key features of thistechnology.

(D) Gear pump: From the extruder 3, melted polymer passes through a gearpump 4. The gear pump 4 delivers a precise volume of material to the diehead 5.

(E) Die head: The die head 5 may be of a spiral mandrel design, and isattached directly after the gear pump 4. This is where polymer is shapedinto a pipe profile, via a tip and die attached at the end. The tip anddie are machined to specified dimensions as necessary.

(F) Curing chamber with UV Irradiators: Directly after the tip and die,the extruded pipe is introduced to a high energy UV irradiator unit 6.This irradiator makes high speed and efficient crosslinking possible.The irradiator unit 6 may comprise, a series of irradiator modules thatare assembled in a row, with each subsequent irradiator module adjacentto the previous module, so that pipe is constantly and consistentlybeing exposed to a controlled level of UV radiation. Other arrangementsof UV lamps may also be used, as would be contemplated by the skilledperson. The irradiator unit 6 may comprise microwave powered UV lamps,for example high efficiency microwave powered lamps.

(G) Calibration fixture: The pipes next enter the cooling unit 8 througha calibration fixture 7, where the pipe dimensions are calibrated andfixed.

(H) Cooling unit: The cooling is conducted by a cooling unit 8. Thecooling unit may comprise a row of spray cooling water baths.

(I) Take up reel: At the end of the production line, typically a coiler9 receives and puts the pipes on reels.

The process is based on the use of a photo-crosslinkable pipeformulation where a photoinitiator (PI) is added. The PI interacts withthe UV irradiation to induce crosslinking of the pipe formulation toform crosslinked polyethylene, i.e., PEX. Along with other additivesmixed in with the formulation (when present), the presence of thephotoinitiator allows for the tubing to be crosslinked throughout theentire pipe wall. The pipes of the invention may be formulated accordingto the compositions and components described herein above. Pipes of theinvention may also be formed using the formulations of the examples.

The twin screws used in the extruder can in principle be constructed intwo different ways, i.e., with a co-rotating or a counter-rotatingdesign. The choice made in the case of the present invention is criticalfor a number of reasons. Ordinarily, it would be expected that acounter-rotating screw would be an efficient material pump relative to asingle screw or a RAM extruder. This means it would be expected toincrease the productivity i.e. line speed. However, we have found that aco-rotating extruder is actually an excellent tool for advanced materialdevelopment and leads to consistent material as well as superior linespeed. We have found the co-rotating twin screws to be excellentmaterial pumps for a material such as a thermoplastic polyolefin.Advantages of the arrangement used in this invention include excellentpipe homogeneity and efficient optimisation of pipe tolerances.

The co-rotating twin screws are configured with a number of screwelements along the screw axis, which may be combined in a number ofdifferent configurations according to the nature of the input raw olefinand additives. The extruder body of typical co-rotating twin screws isconstructed of barrels, which can be seen as separate reactors whichalso provide the flexibility to dedicate one or more specific barrels toperform in certain ways. For example, it is possible to performed directinjection of raw materials into specific zones of the process i.e. intospecific barrels. It is also possible to control the conditions in eachbarrel independently.

The two parallel co-rotating screws consist of a number of designedscrew elements. They are arranged in a modular flexible design withtypically 10 operative zones (barrels). Each barrel can have its owndesign and function (heating, cooling, etc.). The geometry of the screwsis such that the channels are lengthwise open, i.e., there isopportunity for flow in axial direction; flow is possible both upstreamand upstream. The screws are crosswise closed with conveying elements,i.e., multiple parallel paths along machine axis, i.e., no communicationpossible between channels. However, the screws can be made crosswiseopen with kneading elements, which gives opportunity for distributivemixing at expense of pressure generating capacity. The extruder can bedesigned to act as a true and efficient mixer. The co-rotating twinscrews are drag flow pumps with forced displacement at intermesh.

The heat introduced in the process of the invention is fundamentallycontrolled by shear rate, i.e., mechanical energy, optionallysupplemented with heat added from external sources (barrel heating).Fibre, nanoparticles, and/or other fillers may be added directly to theextruder in controlled manner. Fibre for example, may be destroyed by ahigh shear counter-rotating screw if pre-mixed. For a co-rotating screwhowever, the fibre can be added late in the process at the end of thescrew. This opens up the opportunity to produce composite pipes, as ahomogeneous composite, in one single operation. Accordingly in theprocesses of the invention, Fibre, nanoparticles, and/or other fillersmay be added near the end of the screw, thereby reducing the length oftime that these components are exposed to shear forces compared to theother components.

Liquids can be added in a controlled fashion, for example at the end ofthe extruder. A vacuum can be applied in a specific zone, which makes itpossible to add components available as slurries or other liquids. Forexample, the solvent can be removed prior to exit of the extrudate fromthe twin-screw extruder. Pigments, stabilizers, additional highperformance polymers, etc., can also potentially be added sequentiallyin the extrusion process.

The apparatus used in the methods of the invention is flexible in termsof the processing of different materials and dimensions of the producedpipes, for example because the screw design can easily be altered byre-designing individual screw elements, and/or by moving around existingscrew elements. In principle, this means that it is possible to use thesame extruder for different pipe dimensions, with e.g. the same extruderoutput (kilograms/hour; (kg/h)) utilized for all pipe dimensions, whichis unique in the industry. For example, the method of the presentinvention may be performed with an extruder output of greater than 100kg/h, e.g. greater than 150 kg/hr, greater than 200 kg/h, greater than250 kg/hr or greater than 300 kg/h. For example, a method of theinvention may be performed at an extrusion rate of 100 to 500 kg/hr, 150to 450 kg/hr, or 200 to 400 kg/hr. Pipe dimensions may be in the range½″ to 8″ diameter, e.g. in the range ½″ to 4″ diameter.

A ½″ pipe may be extruded in the method of the present invention at arate of about 140 kg/h and extrusion speed of about 30 m/min; while a 4″pipe may be extruded at a rate of about 2 m/min.

In the method of the present invention the extrusion may be performed ata temperature of about 200° C. It is therefore preferred that theadditives used in the methods of the invention, e.g. photoinitiator(s);and/or co-agent(s); and/or anti-oxidant(s); and/or hindered amine lightstabilizer(s); and/or scavengers(s); and/or and processing aids, are notsubject to fuming at 200° C.

The term UV curing is normally used when a combination of aphotoinitiator and an appropriate monomer/oligomer UV lacquerformulation is exposed to ultraviolet radiation to form high performancethin coatings for various commercially established and well knownapplications. The methods of the invention may use highly efficientmicrowave powered UV lamps (for example microwave powered UV lampsprovided by, e.g. Fusion UV Systems). The methods of the invention mayuse microwave powered UV lamps, e.g. highly efficient microwave poweredUV lamps, to provide the UV radiation, which in combination with aphotoinitiator and an optional co-agent facilitates crosslinking of forexample polyethylene to form PEX pipes and tubing.

Assays

Pipes of the invention can be assessed in relation to a number ofparameters using standard tests that would be known to the personskilled in the art. A number of suitable assays are described below andother suitable assays have been described previously under the heading“Pipe Standards and Certifications”. Parameters of interest include NSF61 requirements for residues in drinking water conveyed by pipes andASTM F2023 requirements for chlorine resistance. NSF 61 and ASTM F2023are both incorporated herein by reference in their entirety.

(A) Stabiliser Functionality Assays

Stabiliser functionality testing is a measure of resistance to oxidativedegradation and provides an indication of the long-term performance ofpipes (e.g. PEX pipes), in relation to oxidative degradation, e.g. bychlorine in potable water.

One method for testing the stability of a pipe in the presence of anoxidizing agent is the Oxidative Induction Time (OIT) test. In thistest, a sample of the pipe material is placed in a DSC and held at aconstant temperature of 200° C. in an oxygen-rich atmosphere. The amountof time to the induction of polymer degradation is measured. A longertime before a change in heat flow is observed indicates that the samplewould be relatively more stable in the presence of an oxidizing agent.The test method for the OIT test is ASTM-D3895, which is hereinincorporated by reference in its entirety.

Another test that is performed on pipe samples to evaluate oxidativeresistance is called the Oxidative Resistance (OR) test. This test isdescribed in ASTM F 2023, which is incorporated herein by reference inits entirety. This test places chlorinated water in a pipe under anumber of different combinations of elevated pressure and temperatureuntil the pipe fails. The time until failure of the pipe at thedifferent combinations of temperature and pressure is used to estimatethe life of the pipe.

In addition, another test described in ASTM F 876, which is incorporatedherein by reference in its entirety, is the “Hoop Stress StabilizerTest”. This test is used to demonstrate a pipe material's ability towithstand long term elevated temperature conditions and is described atpoint 7.10 of ASTM F 876. The method provides that the functionality ofa stabilizer of a specific PEX compound shall be verified by hydrostatictesting of pipe made from compound. Test six pipe samples continuouslyfor 3000 h at a hoop stress of 0.70 MPa at 120° C., or for 8000 h at ahoop stress of 0.70 MPa at 110° C. This test is used to demonstrate thespecific compound's ability to withstand long temperature conditions setforth elsewhere in this standard.

When tested in accordance with the ASTM F 876 Hoop Stress StabilizerTest, polyethyene pipes of the invention exceeded the standard anddemonstrated effective stabilization for over 12500 hours. The testedpipes were made in accordance with the co-rotating twin screw method ofthe invention. The tested pipes comprised polyethylene as the structuralpolymer, 0.75% by weight photoinitiator, 0.5% by weight phenolicantioxidant, 0.15% by weight HALS and 1% by weight of a polybutadieneco-agent. This is better than the results obtained previously for otherpipes made using prior art methods and different formulations. Forexample, when tested in accordance with the ASTM F 876 Hoop StressStabilizer Test, polyethylene pipes made using RAM extrusiondemonstrated effective stabilisation for 3,000 to 3,500 hours or forover 5,000 hours.

Without being bound by any theory, it is believed that the improvementin this key performance parameter may be due to the improved homogeneityand distribution of the raw materials in the pipe wall. This effect isassociated with the co-rotating twin screw extrusion method combinedwith photo-induced crosslinking to form a crosslinked polyolefin pipe.It is believed that this combination of features has a synergisticeffect.

(B) Residuals Assay

Pipes of the invention, when tested in accordance with an assay as setout in NSF 61, may have levels of residual that are less than or equalto the levels set out in Table 1.

TABLE 1 Maximum allowance levels of residuals from drinking water pipesChemical Name CAS# NSF TAC (MDWL) EPA MCL NSF SPAC (MAL) NSF STELBenzene 71-43-2  5 ppb 5 ppb 0.5 ppb  Not derived Benzophenone 119-61-9300 ppb  30 ppb 2000 ppb  Benzhydrol 91-01-0 50 ppb 50 ppb 50 ppbp-Hydroxybenzophenone 1137-42-4 10 ppb 10 ppb 10 ppb p-Hydroxybenzhydrol833-39-6 10 ppb 10 ppb 10 ppb p-Formylbenzophenone 20912-50-9 10 ppb 10ppb 10 ppb

A pipe of the invention when tested in accordance with NSF 61 may havelevels of benzene of less than or equal to 5 ppb, benzophenone of lessthan or equal to 30 ppb, benzhydrol of less than or equal to 50 ppb,p-hydroxybenzophenone of less than or equal to 10 ppb,p-hydroxybenzhydrol of less than or equal to 10 ppb, andp-formylbenzophenone of less than or equal to 10 ppb. For example a pipeof the invention when tested in accordance with NSF 61 may have levelsof each of benzophenone, benzhydrol, p-hydroxybenzophenone,p-hydroxybenzhydrol and p-formylbenzophenone of less than or equal to 10ppb; e.g. the level of each of these compounds may be less than 5 ppb.For example a pipe of the invention when tested in accordance with NSF61 may have levels of each of benzophenone and p-hydroxybenzophenone ofless than 8 ppb, e.g. less than 5 ppb.

For example, an NSF 61 analysis for a PEX pipe of the inventioncomprising octadecyl isocyanate scavenger revealed benzophenone at 5.5ppb, benzhydrol at 1 ppb, p-hydroxybenzophenone at 6 ppm and,p-hydroxybenzhydrol at 2.5 ppb.

(C) Pipe Homogeneity Assay

Pipe homogeneity can be determined by analysis of tubing cross-sectionsby FTIR microscopy to determine the distribution of additives in thepolymeric material across the wall of the pipe. The samples are preparedfor analysis by cutting thin (approximately 25 μm thick) cross-sectionsof the polymeric pipe wall with a razor. The cross-sections are thentransferred to a KBr salt plate for analysis with suitable FTIRmicroscope, for example a Nicolet iN10 FTIR microscope equipped with amapping stage and integrated video camera for locating and specifyingareas for analysis. An area map was defined for each sample to includeboth the inner and outer walls. Data is collected and processed toprovide an area map that indicates the distribution of assayed additivesin the pipe wall.

This assay was performed on a PEX pipe made in accordance with theinvention using a co-rotating twin screw extruder and a correspondingPEX pipe extruded by a single screw extruder. The results of the pipehomogeneity assay indicated that both the antioxidant Irganox 1076 andhindered amine light stabilizer Cyasorb 3853 were more homogeneouslydistributed in the PEX pipe of the invention.

(D) Crosslinking Assay

The degree of crosslinking may be measured in accordance with thetesting protocol set out in ASTM F 876 at 7.9. When tested in thismanner, a pipe of the invention may have a degree of crosslinking ofabout 65% to about 89%. For example the degree of crosslinking may bemeasured to be about 70% to about 80%, e.g. about 70% to about 75%. Thedegree of crosslinking may be about 73%, e.g. 73±1% or 73±0.5%.

(E) Components Assay

The components present in a polymeric pipe may be assessed by performingan assay that comprises taking a section of the pipe, extracting thesection of the pipe with an organic solvent under controlled conditionsand analysis the compounds extracted into the solvent using ananalytical technique such as GC/MS.

A suitable protocol for organic extraction is provided by the followingmethod. 1 g of pipe sample is placed in 2 mL of xylene and allowed tocondition at 70° C. for 24 hours. After that, the remaining solid pipesample is removed (for example by filtration) providing an extractcomprising xylene and components extracted from the pipe sample. If adifferent amount of pipe sample is used, the amount of xylene may bevaried in proportion to the amount of pipe sample.

The extract may then be analysed by GC/MS to determine the componentsextracted from the pipe using standard methods. A suitable standardmethod of GC/MS analysis is set out in NSF InternationalStandard/American National Standard for Drinking Water Additives 61-2011(Jun. 10, 2011) (“NSF 61”) at B.7.4.2 “Gas chromatography/massspectroscopy (GC/MS) analysis” and further specified under subheadingsB.7.4.2.1-B.7.4.2.4 on pages B14 to B16, the content of which isincorporated herein by reference.

EXAMPLES Materials and Properties

TABLE 2 Fundamental characteristics of PE resins used in examplesMelting DSC Density Melt Flow Point Crystallinity Supplier (g/cc) (g/10min) (° C.) (%) BasellQ456 0.954 2.20 126.85 70.73 Basell Q 456B 0.9543.00 127.01 69.52 Basell New Resin 0.952 6.50 124.00 66.32 Basell Q 471(Germany) 0.952 10.00 124.56 63.35 Basell Q 471 (lowa) 0.953 9.96 124.0866.24 Borealis HE 1878 0.955 3.70 129.34 74.30 Borealis HE 1878 E 0.94910.00 125.14 62.13 Borealis HE 2550 0.956 6.50 129.35 75.13 PE-RT Basell0.947 12.40 123.53 66.12

TABLE 3 Molecular weights of the PE resins and its distributionsMolecular Weight Supplier M_(w) M_(n) Distribution Basell Q 456 25824533278 7.76 Basell Q 456B 244299 56576 4.32 Basell New Resin 146730 164348.92 Basell Q 471 (Germany) 165033 22434 7.37 Basell Q 471 (lowa) 17076026288 6.826 Borealis HE 1878 228760 24945 9.171 Borealis HE 1878 E186580 34309 5.439 Borealis HE 2550 207212 37133 5.587 PE-RT Basell180752 23164 7.804

Table 2 lists the PE resins used in the examples and lists a number ofproperties of these resins, including density, melt flow, melting pointand crystallinity. Table 3 indicates the molecular weight and molecularweight distribution of the PE resins. The molecular weight and molecularweight distributions were determined using gel permeationchromatography.

Example 1: Direct Injection

A trial was conducted to test the concept of direct injection ofadditives into the extruder. The set up included using a 27 mm twinscrew extruder, a witte gear pump, and a spider-design die head to form½″ tubing. The tubing was then crosslinked by exposure to UVirradiation. The HDPE base resin, along with processing aid, was addedto the extruder via the extruder's feed throat entry point. For allother additives, a blend of 4 components (photoinitiator, co-agent,anti-oxidant, hindered amine light stabilizer), was premixed as ahomogeneous liquid, which was directly injected into the extruder via aninjection port in one of the upstream barrels. Direct injection into theextruder allowed for no pre-mixing of these components with HDPE resinand processing aid. Mixing of these 4 components with HDPE resin andprocessing aid occurred strictly from the mixing elements within thetwin screw extruder.

An initial baseline experiment was performed, which involved pre-mixingof all components, and adding this mix via the feed throat port of theextruder. The pipe formulation was as follows:

Raw Material Weight % PE Resin: Basell Q471 97.96 Photoinitiator:Benzophenone 0.75 Co-agent: TAC 0.75 Antioxidant: Irganox 1010 0.4 HALS:Chimassorb 944 LD 0.1 Processing Aid: FX 9613 0.05

When running the experimental direct injection trial, a feed rate of the2% by weight liquid additives was determined, so the same ratio ofadditives could be obtained as that in the baseline trial. Feed rate ofHDPE and processing aid was also changed to account for this 2% additionof additives, so that an exact comparison could be achieved between thetwo methods of pipe manufacturing. Besides the material introduction,all other processing conditions remained the same for both trials. Theexperimental trial was run for 1 hour, taking samples to cover theentire range.

The level of crosslinking (CCL) for the two tests were as follows.Average CCL achieved in baseline ˜74%. Average CCL achieved for directinjection ˜78%. This represents an encouraging result and may be anindication, based on the CCL's given above, that the distribution of theadditives is more homogeneous when direct injection is used.

Burst, thermal and OIT values comparing the two methods of feeding werevery similar, with OIT values actually being greater for theexperimental vs. the control samples. This also an indication of thatmore homogeneous distribution of stabilizer was accomplished when directinjection was utilized.

Example 2: Pipe Formulations

Formulation 1

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q471(lowa) 25213-02-9 N/A 97.95 Photoinitiator = Benzophenone 119-61-9182.22 0.75 Co-Agent = Triallyl Cyanurate 101-37-1 249.27 0.75Antioxidant = Irganox 1010 6683-19-8 1178 0.40 HALS = Chimassorb 944 LD70624-18-9 2000-3100 0.10 Processing aid = FX 9613 NA NA 0.05 TOTAL 100CCL: 77%Note: NSF 61 not determined.

Formulation 2

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q471(lowa) 25213-02-9 N/A 98.16 Photoinitiator = Benzophenone 119-61-9182.22 0.6 Co-Agent = Triallyl Cyanurate 101-37-1 249.27 0.6 Antioxidant= Irganox 1076 2082-79-3 531.00 0.5 HALS = Chimassorb 944 LD 70624-18-92000-3100 0.1 Processing aid = FX 9613 NA NA 0.04 TOTAL 100CCL: 74%Note: NSF 61 not determined.

Formulation 3

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q471(lowa) 25213-02-9 N/A 97.30 Photoinitiator = Omnipol BP 515136-48-8 7301.00 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853167078-06-0 294-516 0.15 Processing aid = Dynamar FX 9613 NA NA 0.05TOTAL 100CCL: 71%Special Note: Clear Pipe, No fumesNote: No NSF 61 Data available

Formulation 4

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; Borealis HE2550 NA N/A 97.55 Photoinitiator = Omnipol BP 515136-48-8 730 0.75Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00 Antioxidant =Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853 167078-06-0 294-5160.15 Processing aid = Dynamar FX 9613 NA NA 0.05 TOTAL 100CCL: 75%Special Note: Clear Pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=77 ppb4-Hydroxybenzophenone: 127 ppbBenzene: <1 ppb

Formulation 5

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Borealis HE1878 E NA N/A 97.30 Photoinitiator = Omnipol BP 515136-48-8 730 0.75Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00 Antioxidant =Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853 167078-06-0 294-5160.15 Processing aid = Dynamar FX 9613 NA NA 0.05 TOTAL 100CCL: 68%Special Note: Clear Pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=46 ppb4-Hydroxybenzophenone: 85 ppbBenzene: 8 ppb

Formulation 6

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 3; Basell Q 456B (lowa) 9002-88-4 N/A 97.60 Photoinitiator = Omnipol BP 515136-48-8 7300.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853167078-06-0 294-516 0.15 TOTAL 100CCL: 79%Special Note: Clear Pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=135 ppb4-Hydroxybenzophenone: 191 ppb

Formulation 7

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 3; Basell Q 456B (lowa) 9002-88-4 N/A 97.75 Photoinitiator = Omnipol BP 515136-48-8 7300.60 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853167078-06-0 294-516 0.15 TOTAL 100CCL: 79%Special Note: Clear Pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=145 ppb4-Hydroxybenzophenone: 254 ppbBenzene: 1.2 ppb

Formulation 8

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 2; Basell Q456(Iowa) 9002-88-4 N/A 98.00 Photoinitiator = Benzophenone 119-61-9 182.220.75 Co-Agent = Triallyl Cyanurate 101-37-1 249.27 0.75 Antioxidant =Irganox 1010 6683-19-8 1178 0.40 HALS = Chimassorb 944 70624-18-92000-3100 0.10 TOTAL 100CCL: 91%Note: NSF 61 not determined.

Formulation 9

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 96.60 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Nanoclay NA 1.00 TOTAL 100CCL: 69%Special Note: Slight yellow pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17<1 ppb4-Hydroxybenzophenone: 148 ppbBenzene: 3.7 ppb

Formulation 10

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 96.10 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Processing aid = Dynamar FX 9613 NA NA0.00 Nanoclay NA NA 0.50 TOTAL 100CCL: 69%Special Note: Slight yellow pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17<1 ppb NSF limit 10 ppb4-Hydroxybenzophenone: 53 ppbBenzene: 4 ppb

Formulation 11

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.50 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Processing aid = Dynamar FX 9613 NA NA0.00 Nanoclay NA 0.10 TOTAL 100CCL: 71%Special Note: Slight yellow pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17<1 ppb4-Hydroxybenzophenone: 65 ppbBenzene: No Data

Formulation 12

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.35 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Processing aid = Dynamar FX 9613 NA NA0.05 Nanoclay (Nanomer 1.31 PS from NA 0.20 Aldrich, surface modifiedcontains 0.5-5 wt. % aminopropyltriethoxysilane, 15-35 wt. %octadecylamine) TOTAL 100CCL: 71%Special Note: Slight yellow pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17<1 ppb4-Hydroxybenzophenone: =85 ppbBenzene: 3 ppb

Formulation 13

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.05 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Processing aid = Dynamar FX 9613 NA NA0.05 Nanoclay (Nanomer 1.31 PS from NA 0.50 Aldrich, surface modifiedcontains 0.5-5 wt. % aminopropyltriethoxysilane, 15-35 wt. %octadecylamine) TOTAL 100CCL: 69%Special Note: Slight yellow pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17<14-Hydroxybenzophenone: =54 ppbBenzene: TBD (2 Weeks)

Formulation 14

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.10 (Iowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2~2900 1.00 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Octadecyl Isocyanate 112-96-9 295.50 0.50TOTAL 100CCL: 69%Special Note: Clear pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=2.5 ppb4-Hydroxybenzophenone: =6 ppbBenzene: 3 ppb

Formulation 15

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.10 (lowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Co-Agent = Polybutadiene 9003-17-2 ~2900 1.00(Ricon 152) Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb3853 167078-06-0 294-516 0.15 Aluminum Oxide 1344-28-1 101.96 0.50 TOTAL100CCL: 70%Special Note: Clear pipe, Some fumes from Isopropyl alcohol on Aluminumoxide4-Hydroxybenzhydrol: NSF 61 on day 17<1 ppb4-Hydroxybenzophenone: =92 ppbBenzene: 8 ppb

Formulation 16

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.37 (lowa) Photoinitiator = Omnipol BP515136-48-8 730 0.75 Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS= Cyasorb 3853 167078-06-0 294-516 0.15 Krasol NN32 NA ~2100 1.23 TOTAL100CCL: 59%Special Note: Clear pipe, No fumes4-Hydroxybenzhydrol: NSF 61 on day 17=33 ppb4-Hydroxybenzophenone: =34 ppbBenzene: 6 ppb

Formulation 17

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q 471(lowa) 25213-02-9 N/A 98.05 Photoinitiator = Benzophenone 119-61-9182.22 0.50 Co-Agent = 15625-89-5 296.32 0.80 TrimethylolpropaneTriacrylate (TMPTA) Antioxidant = Irganox 1076 6683-19-8 1178 0.50 HALS= Cyasorb 3853 167078-06-0 294-516 0.15 Total 100CCL: 71%Special Note: Clear pipe, rough surface, and some fumesNote: NSF 61 not determined.

Formulation 18

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 3.75; BorealisHE 1878 NA N/A 97.35 Photoinitiator = Omnipol BP 515136-48-8 730 1.00Co-Agent = Polybutadiene Acrylate NA ~2200 1.00 Antioxidant = Irganox1076 2082-79-3 531 0.50 HALS = Cyasorb 3853 167078-06-0 294-516 0.15TOTAL 100CCL: 82%Special Note: Clear pipe, no fumes4-Hydroxybenzhydrol: 30 ppb4-Hydroxybenzophenone: 83 ppbBenzene: <1 ppb

Formulation 19

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q 471(lowa) 25213-02-9 N/A 98.57 Photoinitiator = Benzophenone 119-61-9182.22 0.50 Co-Agent = Triallyl Cyanurate 101-37-1 249.27 0.40Antioxidant = Irganox 1010 6683-19-8 1178 0.28 HALS = Chimassorb 94470624-18-9 2000-3100 0.25 TOTAL 100CCL: 81%Special Note: Clear pipe, fumesBenzhydrol: 3270 ppbBenzophenone: 324 ppbBenzene: 44 ppb

Formulation 20

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5; BasellLP5465X01 25213-02-9 N/A 97.60 (lowa) Photoinitiator = Genopol BP NA 9600.75 Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853167078-06-0 294-516 0.15 TOTAL 100CCL: 35%Special Note: Slight yellow pipe, No fumesNote: NSF 61 not determined.

Formulation 21

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 10; Basell Q471(lowa) 25213-02-9 N/A 97.60 Photoinitiator = Genopol BP NA 960 0.75Co-Agent = Polybutadiene (Ricon 152) 9003-17-2 ~2900 1.00 Antioxidant =Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853 167078-06-0 294-5160.15 TOTAL 100CCL: 33%Special Note: Slight yellow pipe, No fumesNote: NSF 61 not determined.

Formulation 22

Raw Material/Chemical Compound CAS # Mw Wt. % PE; MFI = 6.5 LP5465X01(lowa) 25213-02-9 N/A 97.10 Photoinitiator = Omnipol BP 515136-48-8 7300.75 Co-Agent = Polybutadiene 9003-17-2 ~2900 1.00 (Ricon 152)Antioxidant = Irganox 1076 2082-79-3 531 0.50 HALS = Cyasorb 3853167078-06-0 294-516 0.15 Epoxide 2386-87-0 252.31 0.25 Aluminum Oxide1344-28-1 101.96 0.25 TOTAL 100CCL: 70%Special Note: Clear pipe, No fumes4-Hydroxybenzhydrol: 12 ppb4-Hydroxybenzophenone: 51 ppbBenzene: =6 ppb

Example 3: Line Speeds and Extruder Output

Pipes have been manufactured on a co-rotating twin screw extruder inaccordance with the methods of the invention for various pipes sizes.Exemplary line speeds and extruder outputs were as follows:

½″ pipe: 30 m/min, 142 kg/h

1″ pipe: 23 m/min, 348 kg/h

2″ pipe: 6.5 m/min, 342 kg/h

4″ pipe: 2 m/min, 350 kg/h

These represent a greater than 10-fold increase in line speed (m/min)and output (kg/h) when compared to the typical output of a RAM extrusionmethod.

The invention claimed is:
 1. A polymeric pipe formed from a mixtureconsisting of: a polyethylene structural polymer; a photoinitiator in anamount of 0.02 to 3% by weight; a co-agent in an amount of 0.02 to 10%,by weight; a phenolic antioxidant in an amount of 0.1 to 1% by weight;and optionally a hindered amine light stabilizer in an amount of 0.05 to1% by weight; wherein the photoinitiator is a compound of the followingformula:

wherein: R¹ is —(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)O(C═O)(CH₂)_(q)—; R³ isselected from group consisting of —H, -halo, —OH, —(C₁-C₄)alkyl,—(C₂-C₄)alkenyl, —O(C₁-C₄)alkyl, and —O(C₂-C₄)alkenyl; m is 0, 1 or 2; nis 2, 3, 4, 5 or 6; p is 2, 3, 4, 5, 6, 7, 8, 9 or 10; and q is 0, 1 or2; wherein the co-agent comprises at least one carbon-carbon doublebond; wherein when tested in accordance with the ASTM F 876 Hoop StressStabilizer Test, the pipe demonstrates effective stabilization for over12500 hours; wherein the pipe is a cross-linked polyethylene pipe withthe characteristics of a pipe obtainable by: extrusion of a mixturecomprising the polyethylene structural polymer, photoinitiator,co-agent, phenolic antioxidant, and optional hindered amine lightstabilizer from a co-rotating twin screw extruder to form an extrudedpipe; and cross-linking the structural polymer by irradiating theextruded pipe with UV radiation.
 2. The pipe of claim 1, wherein m and qare both 1, n is 4 and p is 3, 4, 5 or
 6. 3. The pipe of claim 1,wherein the photoinitiator is

wherein r is 2, 3, 4, 5, 6, 7, or
 8. 4. The pipe of claim 1, wherein thephotoinitiator is in an amount of 0.3 to 1.5% by weight.
 5. The pipe ofclaim 1, wherein the co-agent comprises at least two reactivecarbon-carbon double bonds.
 6. The pipe of claim 1, wherein the co-agentcomprises at least one of triallylcyanurate, polybutadiene, ortrimethylolpropane triacetate.
 7. The pipe of claim 1, comprising thehindered amine light stabilizer in the amount of 0.05 to 1% by weight.8. The pipe of claim 7, wherein the hindered amine light stabilizercomprises:

which has a molecular weight of 2000 to 3100 g/mol, or

which has a molecular weight of 3100 to 4000 g/mol, wherein R⁵ is aC₂-C₂₄ alkyl group.
 9. The pipe of claim 1, wherein the antioxidant is aphenolic antioxidant.
 10. The pipe of claim 1, wherein the polyethylenestructural polymer comprises high density polyethylene (HDPE) with amelt flow index (MFI) of at least 2, or with a melt flow index of atleast
 5. 11. The pipe of claim 1, where in the pipe is a cross-linkedpipe.
 12. A method of producing a cross-linked polyolefin pipecomprising: extrusion of a mixture from a co-rotating twin screwextruder to form an extruded pipe; and cross-linking a polyolefinstructural polymer by irradiating the extruded pipe with UV radiation,wherein the extrusion mixture comprises the polyolefin structuralpolymer, a photoinitiator in an amount of 0.02 to 3% by weight, aco-agent in an amount of 0.02-10% by weight, and a phenolic antioxidantin an amount of 0.1 to 1% by weight; wherein the photoinitiator is acompound of the following formula:

wherein: R¹ is —(CH₂)_(m)(C═O)[O(CH₂)_(n)]_(p)O(C═O)(CH₂)_(q)—; R³ isselected from group consisting of —H, -halo, —OH, —(C₁-C₄)alkyl,—(C₂-C₄)alkenyl, —O(C₁-C₄)alkyl, and —O(C₂-C₄)alkenyl; m is 0, 1 or 2; nis 2, 3, 4, 5 or 6; p is 2, 3, 4, 5, 6, 7, 8, 9 or 10; and q is 0, 1 or2; and wherein the co-agent comprises at least one carbon-carbon doublebond.
 13. The method of claim 12, wherein the polyolefin structuralpolymer is one of polyethylene, polypropylene, polybutylene, polyolefincopolymers or any copolymers thereof.
 14. The method of claim 12,wherein the mixture further comprises a hindered amine light stabiliserin an amount of 0.05 to 1% by weight.
 15. The method of claim 12,wherein the cross-linked polyolefin pipe has a degree of crosslinking inthe range of about 60 to about 90%.
 16. The method of claim 12, whereinthe polyolefin structural polymer and at least one component areseparately injected into the extruder; wherein the at least onecomponent is one of the photoinitiator, the co-agent, the phenolicantioxidant, or a combination thereof; and wherein the polyolefinstructural polymer and the at least one component are mixed by a mixingelement of the twin-screw extruder.
 17. The method of claim 12, whereinthe extrusion is performed at an extruder output of greater than 100kg/h.
 18. The pipe of claim 1, wherein the polyethylene structuralpolymer is in an amount of at least 85% by weight.